Pago is a

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...

in the center of

Tutuila Island Tutuila is the main island of American Samoa (and its largest), and is part of the archipelago of Samoan Islands. It is the third largest island in the Samoan Islands chain of the Central Pacific. It is located roughly northeast of Brisbane, Au ...

, the largest island of

American Samoa American Samoa ( sm, Amerika Sāmoa, ; also ' or ') is an unincorporated territory of the United States located in the South Pacific Ocean, southeast of the island country of Samoa. Its location is centered on . It is east of the International ...

in the

South Pacific Ocean South is one of the cardinal directions or compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Proto-Germanic ''*sunþaz ...

. The volcano was formed by

subaerial eruption A subaerial eruption is any sort of volcanic eruption that occurs on the Earth's surface, or in the open air subaerial, 'under the air', and not underwater or underground. They generally produce pyroclastic flows, lava fountains, and lava flows, whi ...

s between 1.54 and 1.28 million years ago. It has been estimated that the volcano was as high as above sea level. Activity on Pago Volcano ended with emplacement of

trachyte Trachyte () is an extrusive igneous rock composed mostly of alkali feldspar. It is usually light-colored and aphanitic (fine-grained), with minor amounts of mafic minerals, and is formed by the rapid cooling of lava enriched with silica and al ...

bodies with ages of 1.03 ± 0.01 Ma. The Pago Volcano

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

was formed 1.27+-0.02 million years ago. The caldera's dimensions are estimated at in length and in width. The southeast part of the caldera makes up

Pago Pago Harbor Pago Pago Harbor on Tutuila Island in American Samoa is one of the world's largest natural harbors. The capital, Pago Pago is located on the inner reaches of the harbor, close to its northwesternmost point. It has the highest annual rainfall of a ...

, one of the world's largest natural harbors. The northwest rim, Maugaloa Ridge, creates the southern border of the

National Park of American Samoa The National Park of American Samoa is a national park in the United States territory of American Samoa, distributed across three islands: Tutuila, Ofu, and Ta‘ū. The park preserves and protects coral reefs, tropical rainforests, fruit bats, ...

References

Volcanoes of American Samoa Tutuila Pago Pago Extinct volcanoes of the United States Polygenetic shield volcanoes {{AmericanSamoa-geo-stub